Many adolescents with acute lymphoblastic leukemia (ALL) have been found to have low bone density by the end of treatment. This can lead to long-term suffering in survivors due to poor bone health. Vitamin D is known to be associated with bone health and previous research has established that Vitamin D insufficiency is very common at diagnosis of ALL and worsens over the course of treatment. Researchers have also learned that a relationship exists between both Vitamin D and fat tissue and ALL and fat tissue.